On bolt wifi module, there is ESP8266 module which operates at the voltage levels of 3.3V. The bolt wifi module is powered by 5V android USB cable. How this happens??
The bolt module has a on-board voltage regulator which converts the 5V signal to the 3.3V, so the ESP8266 operates peoperly and does not get damaged.
The 6V battery may not do any harm if the protection circuits are doing their job, but you have no way of knowing. It will be OK to use a 6V source with some form of current limitation to just add a few minutes of power time, but a long time power could damage device.